How to change the default browser
When I click on a link in an e-mail in Thunderbird it always opens the link in Opera 12.16 but I would like it to open them in Vivaldi. Opera 12.16 is an old version, not supported any more but I used to use it as my main browser and my e-mail client. It does not always work properly with modern web sites. I would remove it from my machine but I occasionally open it to look up old e-mail addresses. Vivaldi will not import the Opera contacts list and to copy all of them into it means doing so one by one. My system is Debian running LDXE.
Opaite Mbohovái (6)
Make sure Vivaldi is your default browser.
That is the problem, I cannot find how to change the default browser.
Thunderbird uses the browser defined as default in your operation system. Research how to set defaults in the operating system you use. It is not a setting in Thunderbird.
I have checked LDXE and opera is not even on the list of choices, Vivaldi-stable is set as the default.
cihutch again. I have tried opening a link from Thunderbird from KDE, and it opens the link with opera also. The default browser in KDE is Vivaldi-stable
Ask in a Debian forum.